I'd agree he has pushed himself back in the '5th' spot which is ideal for someone who can play both sides. However, Slipper can also play both sides and could be argued he could play THP better then HJH (Harry Johnson-Holmes) (Harry Johnson-Holmes) can, and Sio has been doing well. Maths time.
In order
LHP: Bell, Slipper, Sio
THP: Tupou, Ala'alatoa, HJH (Harry Johnson-Holmes) (Harry Johnson-Holmes)
But could easily be this, and considering utility value
LHP: Bell, Slipper, Sio, HJH (Harry Johnson-Holmes) (Harry Johnson-Holmes),
THP: Tupou, Ala'alatoa, Slipper, HJH (Harry Johnson-Holmes) (Harry Johnson-Holmes).